For thermoplastic polyester resins, the fibrous glass enhances the mechanical properties of the resin. Glass filled crystalline resin blends are difficult to mold due to a combination of poor mold flow and shear sensitivity. The crystalline resin has poor melt strength and high shrinkage upon cooling. This makes it difficult to obtain good dimensional tolerances. Typically, extruded blends also have a very rough surface and poor impact strength.
Unfortunately, in such resins, the addition of glass fibers can substantially lower the Izod impact strengths of the fiber reinforced compositions, and, also, substantially reduce the biaxial impact (instrument impact) energies of such compositions.
In order to achieve improved properties, especially impact strength, impact modifiers for poly(alkylene terephthalates) include rubbers of polybutadiene, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, ethylene-propylene rubbers, polyisobutene and polyisoprene.
U.S. Pat. No. 4,096,202 to Franham et al describes modifiers based on acrylic rubbers for improving impact strength without significantly increasing melt viscosity for poly(alkylene terephthalates). The impact modifier is a multi-phase composite interpolymer comprising a cross linked acrylic first stage which also contains graftlinking monomer and a final rigid thermoplastic phase. The crosslinking monomers include poly acrylic and poly methacrylic esters of polyols such as butylene diacrylate and dimethacrylate, trimethylol propane trimethacrylate, and the like; di- and trivinyl benzene, vinyl acrylate and methacrylate, and the like. Among effective graftlinking monomers, which are polyethylenically unsaturated monomers, are allyl group-containing monomers of allyl esters of ethyleneically unsaturated acids such as allyl acrylate, allyl methacrylate, dially maleate, dially fumarate, diallyl itaconate, allyl acid maleate, allyl acid fumarate, and allyl acid itaconate. The resulting multi-phase composite interpolymer is known in the art as an ASA polymer.
U.S. Pat. No. 5,219,915 to McKee et al. relates to glass fiber-reinforced thermoplastic molding materials based on polyesters and graft polymers. The thermoplastic molding materials based on a mixture of polybutylene terephthalate and polyethylene terephthalate as essential components, graft polymers having acrylate rubbers as the grafting base, copolymers of vinylaromatic monomers and acrylonitrile or methacrylonitrile and glass fibers. As set forth, the compositions of both Examples also contained the following additives (in each case in % by weight, based on the total weight of A)+B)): 1.5% by weight of carbon black, 0.1% by weight of talc, 0.8% by weight of pentaerythritol stearate.
U.S. Pat. No. 4,148,956 to Breitenfellner relates to thermoplastic molding compositions of linear polyesters and styrene/ acrylonitrile modified by alpha-methylstyrene and/or acrylates. Disclosed are "inert additives of all types, for example fillers such as talc, calcium carbonate, barium sulphate, SiO.sub.2, kaolin, micromica, wollastonite and metal powders, and reinforcing fillers, such as glass fibers and glass beads, inorganic or organic pigments, optical brighteners, delustering agents, processing auxiliaries, such as lubricants, mould release agents and agents which promote crystallization, flameproofing agents, nucleating agents and stabilizers, such as phosphorus-organic compounds, for example triphenyl phosphite, can be added during working up of the polyester melt or even prior to the polycondensation reaction or during mixing of the polyesters with modified styrene/ acrylonitrile. "
U.S. Pat. No 5,733,959 to Heitz, et al. relates to thermoplastic molding compositions comprise from 20 to 99% by weight of a polyester, up to 90% by weight of which may be replaced by a polycarbonate or a polyamide, from 0.1 to 7% by weight of a carbodiimide. The compositions may contain impact modifiers which are generally copolymers, preferably built up from at least two of the following monomers: ethylene, propylene, butadiene, isobutene, isoprene, chloroprene, vinyl acetate, styrene, acrylonitrile and (meth)acrylates having from 1 to 18 carbon atoms in the alcohol component.
U.S. Pat. No 5,596,049 to Gallucci et al. describes the stabilization of polyesters using epoxy compounds in combination with a catalyst. The disclosed polyester composition comprises a linear polyester resin, a difunctional epoxy compound and a catalyst. The difunctional epoxy compound has two terminal epoxy functionalities. Examples of preferred difunctional epoxy compounds are 3,4-epoxycyclohexyl-3,4-epoxycyclohexylcarboxylate, bis(3,4-epoxycyclohexylmethyl) adipate, vinylcyclohexene di-epoxide, bisphenol diglycidyl ethers, diglycidyl adducts of amines and amides, diglycidyl adducts of carboxylic acids and the like. Especially preferred is 3,4-epoxycyclohexyl-3,4 epoxycyclohexylcarboxylate.
U.S. Pat. No. 4,894,416 to Gallucci relates to low gloss thermoplastic blends with good physical properties consisting of a blend of ASA and a gloss-reducing amount of a glycidyl (meth)acrylate copolymer.
Polyesteramides are described in EP 445 548 B1 as well as in U.S. Pat. No. 5,852,155 to Bussink et al. and in copending patent application U.S. Ser. No. 09/16076, filed Sep. 25, 1998 to Chisholm et al entitled Amide Modified Polyesters.
The prior art focus is to add various ingredients to enhance the properties of the polyester material. However, with this approach, it is difficult to achieve the desired improvement in properties. The addition of one ingredient may improve one property but result in the degradation of another desirable property. As a result, a combination of various ingredients are added which further complicates the production of a consistent product due to the interactions of the various ingredients with one another.
As an example of an additive used to improve properties, it is known to add impact modifiers to polyester resins to improve the ductility or the notched Izod impact strength thereof. However the effect of such impact modifiers on reinforcing polyester resin compositions, such as those containing 20% by weight of reinforcing glass fibers, is not sufficient to result in the desired improvement in heat distortion temperature.
Accordingly, there is a need for simple glass reinforced polyester resin compositions which exhibit consistent and uniform properties together with enhanced properties of improve Heat Distortion temperature which may be tested according to ISO 75-1 test.